- Women of child-bearing potential (WCBP) must have a negative urine pregnancy test (urine HCG) within 48 hours of the methacholine challenge, within 48 hours of the inhaled allergen challenge and on the day of the segmental allergen challenge, as well as fMRI and PET scans. WCBP must agree to use a reliable method of birth control for the duration of the study (reliable methods of birth control can include abstinence, barrier methods, oral contraceptives, injection contraceptives or skin absorption contraceptives).